Topic: Can Carbon Fouled Plugs Be Cleaned & Re-used?

[Popwood]

As I've been trying to sort out over the summer why my plugs 1 & 4 have been carbon fouling, I have often used a brass or sometimes steel brush to clean the carbon and use them again. I'm sure I've done this way more than a dozen times. The plugs were new just a couple months ago and no more than 500 miles. Is there a possibility that cleaning this way and re-use could contribute to the fouling problem? I'm running out of options to solve the problem. At this point I think I'm ready to have the coils bench tested.

It's a stock '75 750K.

Thanks.

[scottly]

I have never had much success cleaning plugs with a wire brush. What has worked best for me was to burn the carbon off with a propane torch: if the porcelain turns brown or white, they can be reused. If the porcelain is a dark gray, they won't work. You can also bead-blast the plugs, but it is difficult to remove beads that get lodged in the nooks and crannies.   

[Popwood]

Thanks, Scottly, and here's a follow up question. You say if after torching the plugs the insulation is gray they won't work. Do you mean they won't fire or they will just continue to carbon foul, or perhaps not work some other way. These plugs will work fine but just carbon foul all over again. I did a couple hundred miles on them a couple weeks ago with no particular issues except they were carbon fouled after the ride. 

[scottly]

If they are gray, they may produce a very weak spark from the center electrode to the fouled porcelain, which won't properly fire the mixture. I've fixed a rich carb, and thought it was still rich until I realized the plugs were fubar. More than once...

[MCRider]

Per Scottly, we used to bead blast them and used them over. I'm not saying this is good, or proper in any way. I'm just saying we did it.

I'm wondering if soda blasting would be better and yield a usable result.

[Popwood]

Well thanks again. I'll switch out and give it a good test. I'd laugh myself to tears if I find this is the solution. But hey, I've learned so much about carbs, timing, dwell, etc. the problem has been a very useful learning experience.

[Popwood]

Per Scottly, we used to bead blast them and used them over. I'm not saying this is good, or proper in any way. I'm just saying we did it.

I'm wondering if soda blasting would be better and yield a usable result.

I have a blaster and can check it out. Thanks MCR.

[Terry in Australia]

Are you using NGK D8EA plugs mate? If so, try some D7EA's, they seem to work much better with the crappy unleaded fuel we run nowadays. Cheers, Terry.

[TwoTired]

The porcelain is abrasive and captures tiny particles of the brass or steel brush on the surface of the porcelain.  These particles are just as conductive as the carbon deposits.

Glass beads can lodge in crevices, then get between piston and cylinder walls.  Not good.

We use a powder for cleaning aircraft spark plugs.  I don't know what it is, exactly.  But, these engines are pretty expensive, the powder type has been used for many years without engine damage.  I expect it is safe for MC engines, too.

http://www.aircraftspruce.com/catalog/topages/splugcleaner.php

Cheers,

[Popwood]

Hey, Terry, I'm using Denso x24es-u. These were highly recommended by Hondaman as the best heat range coming in between D8 and D7. I've read the 7's can be too hot on long rides although I do little of that. I had 7's in earlier this year and was getting better, if not ideal results. But I had probably brushed those a few times, too.

[Popwood]

The porcelain is abrasive and captures tiny particles of the brass or steel brush on the surface of the porcelain.  These particles are just as conductive as the carbon deposits.

Glass beads can lodge in crevices, then get between piston and cylinder walls.  Not good.

We use a powder for cleaning aircraft spark plugs.  I don't know what it is, exactly.  But, these engines are pretty expensive, the powder type has been used for many years without engine damage.  I expect it is safe for MC engines, too.

http://www.aircraftspruce.com/catalog/topages/splugcleaner.php

Cheers,

So, TT, are you saying the conductivity will lead to further fouling perhaps due to weaker spark? Just trying to better understand. Thanks

[Terry in Australia]

Hey, Terry, I'm using Denso x24es-u. These were highly recommended by Hondaman as the best heat range coming in between D8 and D7. I've read the 7's can be too hot on long rides although I do little of that. I had 7's in earlier this year and was getting better, if not ideal results. But I had probably brushed those a few times, too.

No worries mate, it was Hondaman who recommended the D7's to me to use with his ignition on my CB750K0 (it was fouling plugs too) and they work well for me, but we have higher octane pump fuel here in Oz, so that might have been why. Cheers, Terry.

[TwoTired]

The porcelain is abrasive and captures tiny particles of the brass or steel brush on the surface of the porcelain.  These particles are just as conductive as the carbon deposits.

Glass beads can lodge in crevices, then get between piston and cylinder walls.  Not good.

We use a powder for cleaning aircraft spark plugs.  I don't know what it is, exactly.  But, these engines are pretty expensive, the powder type has been used for many years without engine damage.  I expect it is safe for MC engines, too.

http://www.aircraftspruce.com/catalog/topages/splugcleaner.php

Cheers,

So, TT, are you saying the conductivity will lead to further fouling perhaps due to weaker spark? Just trying to better understand. Thanks

Soot fouled plug insulators offer a conductive path alternative for the electrical energy, rather than jumping the spark gap.
Electricity takes the least resistive path.
A metallic coating on the porcelain insulator is just another alternative path to bypass the spark gap.
Both conditions result in spark plugs that don't fire as desired.  A clean un-coated insulator is your only hope of making the spark jump the spark gap and deliver all their energy into the air/fuel mixture.

An easy way to make spark plugs misfire is to take a pencil and mark up the white insulator around the center electrode.  It, in essence, shorts out the spark plug so the energy doesn't jump the spark gap.

[Popwood]

Thanks TT, for the as usual thorough explanation.

[gmonkey]

What worked great for me for de-fouling FRESHLY fouled spark plugs is a cigar torch.  Used to have one on me at all times because the bike that was my primary mode of transportation would flood and foul the plugs if it took too long starting up.  Fortunately it was a twin and the plugs were relatively easy to get at so, after some practice (which I got on a regular basis), I could get the plugs out, torched and back in in a few minutes.